Vehicles used for hauling trailers must be capable of sustaining the axle load of the trailer and capable of accommodating the type of hitch provided by the trailer. Further, the towing a trailer can restrict the maneuvering of the combined vehicle and trailer particularly while backing up. The vehicle and trailer combination typically also presents tracking and traction issues. The prior art provides a number of attempts to overcome these difficulties. A common method is to incorporate a convertor dolly which provides at least one axle, a specific type of hitch suitable for accommodating the trailer to be towed, and a tongue for attachment to the prime mover vehicle. The convertor dolly reduces the axle load of the prime mover vehicle and facilitates the prime mover vehicle to provide principally a pulling force. Convertor dollies are arranged such that the dolly functions as an extension of the rear of the prime mover vehicle such that the convertor dolly typically does not rotate or pivot around the prime mover tow point thereby keeping the frame of the dolly and hence the alignment of wheels of the dolly fixed in the direction of the rear of the prime mover vehicle. Prior art convertor dollies have several distinct disadvantages in that the combined trailer, dolly, and prime mover vehicle is difficult to reverse and that the dolly wheels are fixed in the forward position matching the rear wheels of the prime mover vehicle. Because the wheels of a typical convertor dolly do not turn in a steering motion, the combined prime mover vehicle rear wheels and the dolly wheels necessarily bind against the pavement during turning maneuvers thereby reducing control, traction, and stability during turning. Similarly, reversing maneuvers are particularly difficult with prior art convertor dollies because the dolly wheels are not steerable thereby making turning maneuvers while backing up almost impossible.
Further, prior art convertor dollies have fixed hitch types for accommodating a specific type of trailer hitch. The fixed hitch types are typically fixed in position relative to the dolly axle thereby limited the adjustability the load on the prime mover vehicle rear axle.
Traction is essential for full maneuvering control. The combination prime mover and dolly are rigidly fixed together, in part, so that when in combination with a trailer there is no double articulation of the assembly. A disadvantage of this arrangement is that the prime mover and dolly assembly can be long. The length becomes important when considering the effect on the assembly when traveling over non-level undulating surfaces. As the combination has a least three axles and the frames are fixed relative to each other, traction can be lost on an axle as it is lifted away from a road surface by the other axles.
What is needed is an improved convertor dolly capable of providing steering tracking of the dolly wheels in response to the prime mover vehicle turning maneuvers thereby providing improved handling, traction, and maneuverability and being of particular importance to permit backup maneuverability while also providing the ability to adapt a variety of trailer hitch types for hauling.